Selective degeneration of axons occurs during neuronal development and is also seen in many neurodegenerative situations. However, exactly how a neuron can activate and compartmentalize this degenerative pathway to destroy its axon without putting the rest of the cell at risk is unclear. Understanding the molecular mechanism of axonal loss is important for developing new therapeutic interventions to treat axon degeneration in pathological conditions. This project will explore the molecular intersection between apoptotic pathways that destroy an entire neuron and pathways that mediate axon-specific degeneration. Caspase-6 was recently shown to be active in degenerating axons. This proposal will test the hypothesis that Caspase-6 actively contributes to axon-specific demise through a stimulus-dependent mechanism that involves components of the intrinsic (mitochondrial) apoptotic pathway. The first aim will investigate the importance of Caspase-6 as a generalized mechanism of axon degeneration. Specifically, Caspase-6 activation will be examined in multiple models of axon degeneration in vitro and in vivo. Importantly, microfluidic technology will be utilized to localize insults to axons, therefore allowing the study of axon-specific degeneration without affecting the neuronal cell body. The second aim will examine the importance of known apoptotic components (e.g., Bax, cytochrome c, Caspase-9, Apaf-1, Caspase-3) in Caspase-6 activation during axon-specific degeneration. This aim will also test the hypothesis that XIAP, an endogenous inhibitor of caspases, protects the neuronal cell body by restricting caspase activity to the axon during axonal degeneration. PUBLIC HEALTH RELEVANCE: Neurons are able to selectively destroy their axons - a large extension from the cell body that is required for neuron function - without putting the rest of the cell at risk. The experiments proposed in this grant will help identify the molecular mechanism by which axons degenerate and determine how neurons are able to compartmentalize destructive mechanisms to axons while keeping the rest of the cell intact. This information could lead to new therapies that specifically prevent axon degeneration during neuronal injury or disease.